This proposal investigates the effects of insulin and leptin on the glucose sensitivity of glucose sensing neurons (GSNs) in the hypothalamic arcuate nucleus (ARC). The overall objective is to gain a clear understanding of (a) how the glucose sensitivity of ARC GSNs is regulated by ambient levels of insulin and leptin and (b) how the dysfunctional signaling pathways for these neuronal signals seen in obesity and type 2 diabetes mellitus (T2DM) alter the function of ARC GSNs. The 2 hypotheses in this proposal directly address these issues. Hypothesis I is that insulin and leptin modulate the glucose sensitivity of ARC GSNs. The corollary to hypothesis I is that the dysfunctional insulin and leptin signaling which occurs during obesity and T2DM contributes to the impaired glucose sensitivity of ARC GSNs. Hypothesis II is the nitric oxide (NO) signal transduction pathway is a point of convergence in the regulation of ARC GSNs by glucose, insulin and leptin. The first set of experiments proposed herein will define the glucose concentration response relationships for ARC GNSs in the presence of insulin and leptin. We will also explore the cellular pathways underlying the interactions between glucose, insulin and leptin so that the mechanisms that underlie any change in responsiveness can be understood. We will then determine whether or how the responses are altered during obesity and T2DM. The second set of experiments will examine the hypotheis that NO provides a novel signal transduction pathway at which glucose, insulin and leptin signaling converges. We will also test the hypothesis that NO provides a mechanism for the glucose-induced presynaptic modulation of neuronal activity which we have observed. These studies will provide important information regarding the way that the brain integrates signals of overall energy status and how this system is altered during obesity and T2DM. This will facilitate the development of new and effective treatments for these serious diseases of the modern world.